In 2006, Bradley Waldroup murdered his wife’s friend and attempted to kill his wife during what was described as intentional and premeditated actions spurred by a domestic dispute. A forensic psychiatrist discovered that Waldroup possessed a variant of a rare enzyme deficiency that can cause depression that, when added to his history of severe child abuse, set the stage for the possibility of him becoming a violent adult. Evidence of this gene-environment combination proved pivotal to jurors, who declined to sentence Waldroup to death.

A new study by Professor Deborah Denno examines the role of behavioral genetics evidence in criminal cases and suggests that, not only is much of the controversy surrounding the admission of genetics-related evidence unwarranted, but also that the use of such evidence has been greatly misunderstood.

Denno presented the study at a recent symposium based on publication of an article in the Michigan State Law Review. The piece has been recommended by the Getting Scholarship into Court Project, sponsored by the National Association of Criminal Defense Lawyers, as a "must read" article that will be especially useful to courts and practitioners.

The longitudinal study covers Denno's research on all criminal cases that used behavioral genetics evidence between 1994 and 2011. "It offers a rich context for determining how the criminal justice system has been handling genetics factors for nearly two decades," said Denno.

Key findings in the study include the following:

Courts/judges increasingly allow behavioral genetics evidence in the majority of cases in which defense attorneys attempt to offer it.

Behavioral genetics evidence is almost exclusively offered by the defense.

Such evidence is often used to validate conditions already admissible in courts.

With rare exceptions, this evidence has not been used against defendants. At most, it becomes an effective tool—along with other evidence—in rendering a defendant ineligible for the death penalty.

The evidence is being accepted by judges for a wider variety of mental and behavioral disorders.

Behavioral genetics evidence is used almost exclusively used in death penalty cases, primarily in two ways:

To support claims of ineffective assistance of counsel for neglecting such evidence; or

To provide proof and diagnosis of a defendant’s mitigating condition

According to Denno, there has been a slow but noticeable shift over the last two decades and primarily within the last four years of judges allowing behavioral genetics evidence into court.

"Behavioral genetics evidence seems to have reached a status commensurate with other kinds of evidence without the baggage of abuse with which it has been typically associated," she said.